Mark Twain Lake

Mark Twain Lake is a reservoir located in Ralls and Monroe Counties in the U. S. state of Missouri. It was created by the Clarence Cannon Dam (formerly called Joanna Dam) impounding the Salt River and is located about 20 mile (32 km) southwest of Hannibal. The lake was named for Missouri author Mark Twain and part of the area around it is Mark Twain State Park. The village of Florida, the birthplace of Mark Twain, is mostly surrounded by the lake.

In 1937 the Joanna Dam project was first proposed as an answer to many years of flooding by the Salt River. With support and expertise of many, including Representative Clarence Cannon, the multi purpose project was authorized by Congress in the Flood Control Act of October 1962. The dam and the lake offer multiple benefits to Northeast Missouri including: hydroelectricity, flood Control, recreation, fish and wildlife conservation, water supply (shortage of existing ground water), navigation. The dam was dedicated in 1984. Johnny Cash played at the dedication ceremony.

Clarence Cannon Dam is a 138 feet (42 m) high and 1940 feet (591 m) long combination concrete gravity embankment dam. The dam contains of concrete and of earth fill. The dam contains a hydroelectric power plant, with two generators, capable of producing up to of power, or enough to supply a town of 20,000 people. When both units are operating at capacity, as much as of water pass through the turbines each minute. A regulation dam, located 9.5 mile (15 km) downstream from the main dam, creates a storage pool that can be used for pumped storage hydroelectricity. When demand for electricity is low, power from other sources can be used to pump water back from the tailwater to the lake. This water can then be re cycled through the turbines when energy is in high demand. this site, known as the Crigler Mound Group, is listed on the National Register of Historic Places.